Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
Typical image forming apparatuses, such as printers and multi-function peripherals (“MFPs”), use a pulse-surface-area modulation method or a pseudo modulation method (e.g. ordered dithering method, error diffusion method, or the like), in which a multi-valued color is artificially represented with a set of dots, to perform an image process.
In this image process, however, if the number of gradation steps is limited, for example, to improve stabilization, a visual discontinuity may occur in the image. This visual discontinuity may cause so-called “contouring,” significantly reducing image quality.
To solve this problem of contouring, various technologies have been proposed. For example, to perform correction mainly to improve gradation characteristics, noise is added to a portion at which continuity is lost in input/output characteristics or a reference value in an error diffusion method is changed.
However, contouring may appear when the same color value continues in a certain area. It is not possible to prevent this contouring efficiently with the above technology.
In other words, it has not been possible to solve the problem that contouring occurs when the same color value continues with the above technology.
If correction or process is performed more than necessary to prevent contouring, there has been a risk that image quality would be lowered.
The present disclosure relates to an image processing apparatus that prevents the occurrence of contouring by irregularly performing fine modulation on tentative output color values obtained by color conversion without impairing image quality.